The present inventors have previously described the preparation of 7-nitroindoline-caged neuroactive amino acids, particularly the 5-methoxycarbonylmethyl and 4-methoxy compounds 1 and 2 that are able to release L-glutamate on a sub-μs time scale in response to a rapid pulse of near-UV light (typically in the ˜300-350 nm range).1-3 Evaluation of the pharmacology of these reagents showed that the glutamate conjugates 1 and 2 had no evidence of binding to glutamatergic receptors,4 making them particularly suitable as reagents to investigate synaptic function in neuronal cells and both reagents have become established as experimental tools for this purpose.5

The overall photocleavage reaction of these compounds in aqueous solution is shown in Scheme 1.

In contrast to these glutamate reagents, conjugates of γ-aminobutyrate (GABA) and glycine corresponding to structure 1, i.e. compounds 3 and 4, were found to show binding to their relevant GABA or glycine receptors on neuronal cells, and the response to photolytic release of GABA or glycine though useful was therefore blunted.4 
WO 00/55133, WO 02/083639 and WO 2004/085394 describe the present inventors' work in developing novel photoreleasable 7-nitroindoline compounds and improved methods for their synthesis.
However, it remains a challenging problem in the art to provide compounds that cage effectors such as neurotransmitters and amino acids that are capable of reducing or abolishing the interaction of the effector with its receptor. This is a particular problem as the caged compounds also need to be chemically robust enough to be used under the conditions found in biological systems and in experimental electrophysiological research.